steps to evaluate link contracts

[Markus Sabadello <markus.sabadello@gmail.com>]

I'm trying to implement link contracts on the server side according to the patterns at:
http://wiki.oasis-open.org/xdi/PdxExample

The challenge is that for a given

- sender XRI (e.g. =!2222.xxxx.yyyy.zzzz!8888.ssss.tttt.uuuu)
- operation XRI (e.g. $get)
- operation address (e.g. =!1111.aaaa.bbbb.cccc!9999.xxxx.yyyy.zzzz/+tel)
- graph containing link contracts

... a decision has to be made whether to allow the operation or not.

The assumption is that the sender XRI has already been authenticated with a signature, password or some other means, so this only about authorization, not authentication.

I've come up with the following decision algorithm:

1. Find all link contract roots:
   A link contract root is a subject that ends in $has and has a /$is$a/$has statement.

2. For each link contract root, find all link contracts:
   This is done by following the /$has$a statements from the link contract roots.

   A link contract is a subject with a /$is$a statement whose reference ends in $has.

3. For each link contract, find the list of link contract parties:
   This is done by appending $a to the subject of the link contract root.

   A list of link contract parties is a subject with a /$is$a/$a statement.
   The actual parties to the link contract can be found on the /$is$has predicate.

If the following conditions are true:
- The link contract contains the operation XRI in question (e.g. $get)

- The link contract contains the operation address in question, or a superset of that address (e.g. =!1111.aaaa.bbbb.cccc!9999.xxxx.yyyy.zzzz$1/+tel or =!1111.aaaa.bbbb.cccc!9999.xxxx.yyyy.zzzz$1)
- The list of link contract parties includes the sender XRI of the message in question (e.g. =!2222.xxxx.yyyy.zzzz!8888.ssss.tttt.uuuu)

... then allow the operation.

... otherwise proceed to the next link contract / link contract root until none are left, then deny the operation.

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Pretty complicated, but I can see it working.

I'm attaching a PDF with a subset of the PdxExample.
All the parts I need for the above decision making process are highlighted in YELLOW.

There are however some questions I have,
- What's the point of having the parts that are highlighted in GREEN? I don't seem to need those.

- Does the decision making process have to include the parts highlighted in BLUE? In other words, does it matter who issued the link contract?

Markus

linkcontracts.pdf